1. Field of the Invention
This invention relates to the art of silver recovery and, more particularly, to a gravity flow apparatus for use in the recovery of silver from spent photographic fixer solution.
2. Description of Prior Art
A number of devices employing containers for recovering silver from spent fixing solutions in photographic paper and film processes are known in the industry. These devices generally entail passing the solution containing silver salts through a metal which is above silver in the electromotive force series. The resultant chemical replacement action causes silver to be deposited within the container as the metal is dissolved. When the metal is exhausted, the contents of the container are processed at a refinery to recover the silver therein.
U.S. Pat. No. 3,369,801, which issued to Harlan G. Hartman on Feb. 20, 1968, discloses a vessel in which the solution flows downward through a core tube to the bottom of the vessel and thence upward through steel wool to an outlet in the top of the vessel. The chemical reaction referred to above results in the deposition of silver within the vessel as the steel wool dissolves.
Window screen is used as the filler material in U.S. Pat. No. 3,630,505, which issued to Byron R. MacKay on Dec. 28, 1971. The screen wire is therein said to be an improvement because steel wool fibers are quite small in diameter and are easily dissolved. As a consequence, large openings providing less resistive paths are created, permitting the solution to bypass the filler material and to exit the vessel with the silver remaining in solution. In U.S. Pat. No. 3,630,505 the solution fluid is directed through a flow path from the inside surface of the container, through the screen, and upward from the bottom of the core tubing.
U.S. Pat. No. 3,655,175, which issued to Victor Zeleny, et al on Apr. 11, 1972, discloses a cannister in which the solution flows from the bottom of the core tube upward through metal shavings and a bed of neutralizing material of alkaline earth metal carbonates. U.S. Pat. No. 3,655,175 also discloses horizontal spacers or baffles separating the layers of shavings to prevent short circuitry of the solution as it flows upward through the filler material.
U.S. Pat. No. 3,840,217, which issued to Michael T. MacKay on Oct. 8, 1974, discloses a plastic container with influent and effluent liquid passages in the form of T-connectors in its lid. The lower end of the influent tube is a T-shaped baffle for dispersing the influent solution. A U-shaped tube is connected between the influent and effluent connectors to accomodate solution overflow. Furthermore, the U-shaped tube is removable from the effluent connector to permit testing of the effluent solution to determine whether silver is being efficiently removed from the solution.